1. Field of the Invention
The invention relates in general to algorithms for use in forming three-dimensional objects by solid freeform fabrication techniques such as stereolithography. In particular, the present invention relates to an improved algorithm capable of automatically detecting geometrical configurations of an object that require special build parameters and automatically selecting those parameters for a range of Z-values without intervention by the operator.
2. Description of the Prior Art
Many algorithms have been proposed previously to control the forming of a three-dimensional object in a layer by layer manner by solid freeform fabrication techniques. Some solid freeform fabrication techniques, herein referred to as SFF, include stereolithography, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. One recent algorithm is disclosed in U.S. Pat. No. 6,159,411 to Kulkarni et al. wherein a style wizard determines a general build style for a three-dimensional object to be formed in response to answers to a series of questions by an operator. The objective of the algorithm is to simplify the selection process as much as possible in order to prevent or eliminate operator error in deriving build parameters for the three-dimensional object.
A three-dimensional object formed according to improperly selected build parameters often results in an unacceptable part. In stereolithography, sometimes the object collapses on itself during the build process or the recoater blade tears up sections of the object creating a plurality of strings of solidified material in the resin vat. Such failures not only waste operation time, but also create additional maintenance time, as the solidified material floating in the resin vat must be removed. Eliminating object collapses and failures is highly desirable.
Build failures not only occur due to the improper selection of a general build style for the three-dimensional object, but also due to failure to identify special geometric features on the object that may require unique parametric treatment prior to building. Generally, these special geometric features cannot be built successfully by the default values of general build style parameters and require special build parameters to be assigned. Undesirably, the operator must identify these special geometric features before the object is formed to assign the special build parameters, and if missed, build failure typically occurs.
There are currently four categories of special geometric features, or special build types that, when present, need to be identified on an object to be formed by stereolithography. These special build types are 1) Trapped Volumes, (2) Large Flat Up-facing Surfaces, (3) Near Flat Down-facing Surfaces, and (4) Delicate Features. Trapped Volumes and Large Flat Up-facing Surfaces cause problems that are generally solved by adjusting re-coating parameters as discussed in U.S. Pat. No. 5,945,058 to Manners et al. Near Flat Down-facing Surfaces sometimes cause border delamination and layer delamination problems when these features are built by default values of the general build style parameters. These problems can be solved by adjusting build parameters such as those related to support spacing, fill scanning, and border scanning, and the like. Delicate Features can cause problems because the re-coating parameters associated with most general build styles operate too vigorously, often knocking off the delicate feature as it is being built. Slowing down the re-coating parameters, or the like, can solve this problem. Extensive work has been done to develop different parameter sets for each of the special geometric conditions in order to solve their associated problems.
However, in order to properly form objects having any of these geometric configurations present, the operator must manually identify them. These special build types cannot be selected until the data representing the three-dimensional object to be built is imported into the platform and a Z-axis established for building the object prior to slicing. Undesirably, the special geometric features must then be visually identified by the operator who must manually assign one of the special build types to the range of Z-values in which the special feature resides. If the operator is inexperienced or inattentive, the assignment of a necessary special build type can be overlooked, which typically results in build part failure and the generation of long strands of solidified spaghetti-like material in the resin vat.
Although a special build type can be manually assigned to a range of Z-values of an object to be formed, problems can arise when two or more special build types are present within the same range of Z-values. For example, if a trapped volume and a delicate feature are located within the same range of Z-values, only the parameters associated with the last build style assigned will be used. Often, these parameters may not be appropriate in forming the object in the areas where the other special build type exists and can result in part failure. Currently, the only method to overcome this situation is for the operator to manually select each individual build and/or re-coating parameter. Only experienced and skilled operators are able to successfully recognize these conditions and select appropriate parameters. Thus, novice operators cannot successfully build many sophisticated geometric configurations without some trial and error. This is undesirable.
Thus, there is a need to increase the probability of a successful build by reducing the number of manual decisions by the operator to select the build parameters for an object. There is also a need to more fully automate the process of determining all the build parameters necessary to build any three-dimensional object desired.
These and other difficulties of the prior art have been overcome according to the present invention.
The present invention provides its benefits across a broad spectrum of solid freeform fabrication (SFF) techniques. While the description which follows hereinafter is meant to be representative of a number of such applications, it is not exhaustive. As will be understood, the basic apparatus and methods taught herein pertaining to stereolithography can be readily adapted to many uses. It is intended that this specification and the claims appended hereto be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed.
It is one aspect of the present invention to eliminate operator error as much as possible when build parameters are selected for forming a three-dimensional object layer by layer by a SFF process such as stereolithography.
It is another aspect of the present invention to automatically identify special build types within a given three-dimensional object to be formed.
It is still yet another aspect of the present invention to automatically assign a set of alternate parameters for each special build type identified in a given three-dimensional object to be formed.
It is a feature of the present invention to identify special build types within a range of Z-values of an object by processing the data descriptive of the object by a computer control system after orienting the object in accordance with a Z-axis.
It is another feature of the present invention to identify more than one special build type within a particular range of Z-values of an object by processing the data descriptive of the object after orienting the object in accordance with a Z-axis.
It is still another feature of the present invention to automatically select alternative parameters within a range of Z-values having more than one special build type identified within the range.
It is an advantage of the present invention that build failures are substantially minimized by automatically identifying special build types on an object and by automatically determining the alternative parameters for building the object where the special build types have been identified.
It is another advantage of the present invention that nearly any complex three-dimensional object can be successfully built with minimal expertise required of the operator.
These and other aspects, features, and advantages are achieved/attained in the apparatus of the present invention that employs a memory for selecting a general build style, a memory for receiving data representing the three-dimensional object, and a control computer programmed to process the selected general build style and object data to identify at least one special build type within a range of Z-values for the object. The apparatus further comprises a coating system for forming a layer of build material according to at least one parameter from the general build style or the special build type, and an exposure system for selectively applying prescribed stimulation to the layer according to at least one of the parameters of the general build style or the special build type.
The method of the present invention comprises a) determining a general build style for the object, b) providing data representing the three-dimensional object to be formed, c) orienting the data in accordance with a Z-axis, d) identifying at least one special build type for at least one range of Z-values of the object, e) forming a layer of build material according to at least one parameter from the general build style or special build type, f) exposing the layer of build material to prescribed stimulation to form successive lamina of the three-dimensional object according to at least one parameter from the general build style or special build type, and g) repeating the steps of forming and exposing the layer in order to form the three-dimensional object.
The apparatus and method is unique because the data representing the three-dimensional object is analyzed by a computer control system programmed to identify the more than one special build type within a given range of Z-values of the object. In one embodiment, conflicting parameters from two or more special build types identified within a range of Z-values are compared and the most conservative value is selected and assigned to a composite special build type for the range of Z-values. In another embodiment, all the parameters associated with one of the special build types identified are selected according to a special build type hierarchy. In yet another embodiment, the parameters of the two or more special build types are compared to corresponding parameters of the general build style, and the parameters of the special build type having the highest priority parameter change according to a special parameter hierarchy are selected. In one embodiment the alternative parameters for the special build types are predetermined parameter sets. Preferably the parameter sets are stored in a library of special build types for retrieval, as needed. In addition, it is desirable to have one parameter set for each special build type associated with each general build style available. However, in an alternative embodiment the values of the alternative parameters are calculated by a computer control system according to a linear, exponential or logarithmic relationship that can take into account the severity of the geometric condition.